Abrasion resistant silicone coated polycarbonate article

ABSTRACT

A shaped non-opaque coated polycarbonate article having improved abrasion and chemical solvent resistance comprising a polycarbonate substrate having disposed on the surface thereon a non-opaque primer layer comprised of a thermoplastic acrylic polymer containing functional groups and disposed on said primer layer a non-opaque top coat comprised of a colloidal silica filled thermoset organopolysiloxane.

This invention relates to non-opaque abrasion and chemical solventresistant silica filled organopolysiloxane coated shaped polycarbonatearticles wherein the silica filled organopolysiloxane top coat isuniformly and tenaciously adhered to the polycarbonate substrate and toa process for producing such an article. More particularly, the presentinvention relates to a silica filled organopolysiloxane coatedpolycarbonate article having a primer layer disposed between thepolycarbonate substrate and the silica filled organopolysiloxane topcoat comprising a thermoplastic acrylic polymer containing functionalgroups. The process for producing said article comprises priming thepolycarbonate substrate with an adhesion promoting thermplastic acrylicpolymer containing functional groups by forming a film of said acrylicpolymer on the surface of the polycarbonate article; applying onto theprimed surface a further curable silica filled organopolysiloxane topcoat composition; and curing the silica filled further curableorganopolysiloxane to form a uniform and tenaciously adhered abrasionand chemical resistant top coat.

BACKGROUND OF THE INVENTION

The use of transparent glazing materials utilizing polycarbonate resinas a structural component for windows, windshields and the like are wellknown. While these polycarbonate resins are easily fabricated into thedesired shape and have excellent physical and chemical properties, suchas being less dense than glass and having more breakage resistance thanglass, their abrasion and chemical solvent resistance is relatively low.

In order to overcome this relatively low abrasion resistance and tootherwise improve the surface characteristics of the polycarbonatesubstrate, various coatings have been applied to the polycarbonateresins. U.S. Pat. No. 3,582,398 describes a fabricated polycarbonatepart having improved optical properties consisting of a polycarbonatesubstrate having a transparent coating thereon consisting of athermoplastic polymethylmethacrylate. U.S. Pat. No. 4,061,652 describesa coating for polycarbonate resins comprised of (i) an acrylic resinwhich is a mixture of olefinically unsaturated organic monomers incombination with an acrylic polymer, and (ii) certain urethanes ofhydroxybenzotriazoles and hydroxybenzophenones in combination withcertain catalysts. U.S. Pat. Nos. 3,451,838, 3,986,997 and 4,027,073disclose organopolysiloxane coating compositions and techniques for theapplication of these organopolysiloxane coatings onto polycarbonatesurfaces. While these coatings have many desirable properties, e.g.,they are hard, abrasion resistant, and chemical solvent resistant, theseorganopolysiloxane coatings do not in all instances possess therequisite degree of uniform adherence to and durability on thesepolycarbonate surfaces. U.S. Pat. No. 3,707,397 describes a process forproviding a hard coating on, inter alia, polycarbonate articles, saidprocess including priming the polycarbonate surface with an adhesionpromoting thermosettable acrylic and applying an organopolysiloxane ontothe primed surface. An article produced by this process, whilepossessing acceptable initial adherence of the organopolysiloxane to thesubstrate, suffers from the disadvantage that upon prolonged exposure toweathering, and particularly to sunlight, the organopolysiloxanegenerally tends to lose its initial adherence to the substrate.Furthermore, as the thickness of the thermoset acrylic primer layerincreases, the abrasion resistance of the coated article generallydecreases. There thus remains a need for non-opaque polycarbonatearticles having uniformly, tenaciously and durably adhered abrasion andchemical resistant coatings thereon, and it is a primary object of thepresent invention to provide such articles and a relatively simple andeconomical process for producing these articles.

DESCRIPTION OF THE INVENTION

This invention relates to non-opaque colloidal silica filledorganopolysiloxane coated polycarbonate articles having a thermoplasticfunctional group containing acrylic polymer adhesion promoting primerlayer disposed between the polycarbonate surface and theorganopolysiloxane and to a process for producing these articles.

In the practice of the present invention, prior to the application ofthe silica gel organopolysiloxane coating to the polycarbonate surface,the surface is first primed by the application thereon of a primer layercontaining a thermoplastic acrylic polymer having functional groups.

The aromatic carbonate polymer of the instant invention has recurringunits of the formula: ##STR1## wherein each --R-- is selected from thegroup consisting of phenylene, halo-substituted phenylene and alkylsubstituted phenylene; and A and B are each selected from the groupconsisting of hydrogen, hydrocarbon radicals free from aliphaticunsaturation and of radicals which together with the adjoining ##STR2##atom form a cycloalkane radical, the total number of carbon atoms in Aand B being up to 12.

The aromatic carbonate polymer of this invention may be prepared bymethods well known in the art and as described in U.S. Pat. No.3,989,672 all of which are incorporated by reference.

Also, included herein are branched polycarbonates wherein apolyfunctional aromatic compound is reacted with the dihydric phenol andcarbonate precursor to provide a thermoplastic randomly branchedpolycarbonate wherein the recurring units of formula I. containbranching groups.

The preferred polycarbonate resins may be derived from the reaction ofbisphenol-A and phosgene. These polycarbonates have from 10-400recurring units of the formula: ##STR3##

The polycarbonate should have an intrinsic viscosity between 0.3 and1.0, preferably from 0.40 to 0.65 as measured at 25° C. in methylenechloride.

The term "thermoplastic acrylic polymer having functional groups" asused herein is meant to embrace within its scope those thermoplasticpolymers resulting from the polymerization of one or more substitutedacrylic or methacrylic ester monomers represented by the general formula

    CH.sub.2 ═CY--COOR.sup.1 X                             III.

wherein Y is H or a methyl radical; R¹ is an alkyl group, preferably analkyl group containing from 1 to about 20 carbon atoms; and X is ahydroxyl, carboxyl, amine, epoxide, amide, SH, SO₃ H, COOR² and Si(OR³)₃group, wherein R² and R³ are alkyl groups, preferably alkyl groupscontaining from 1 to about 20 carbon atoms. Copolymers resulting fromthe polymerization of two or more of substituted acrylic ester andsubstituted methacrylic ester monomers are also included within the term"thermoplastic acrylic polymer having functional groups" as it appearsherein. Also included within the term "thermoplastic acrylic polymerscontaining functional groups" as used herein are copolymers resultingfrom the polymerization of acrylic acid ester, i.e., acrylate, monomersand/or methacrylic acid esters, i.e., methacrylate, monomers with theaforedescribed substituted acrylic ester or substituted methacrylicester monomers. Exemplary acrylate and methacrylate monomers which canbe copolymerized with the substituted acrylic ester and/or substitutedmethacrylic ester monomers to form the thermoplastic acrylic polymerscontaining functional groups include methyl acrylate, ethyl acrylate,butyl acrylate, 2-ethylhexylacrylate, methyl methacrylate, ethylmethacrylate, butyl methacrylate, hexyl methacrylate, etc. Examples ofcopolymers of this type include copolymers containing ethyl methacrylateand hydroxyethyl methacrylate, ethyl methacrylate andγ-methacryloxypropyltrimethoxysilane, methyl acrylate and hydroxyethylacrylate, and the like.

The polymerization of the above monomeric substituted acrylate andmethacrylates to provide the thermoplastic acrylic polymer havingfunctional groups useful in the practice of the present invention may beaccomplished by any of the well known polymerization techniques.

Typical substituted acrylic and methacrylic ester monomers representedby formula III are set forth in Table I.

TABLE I

CH₂ =C(CH₃)COOCH₂ CH₂ OH

CH₂ =CHCOOCH₂ CH₂ OH

CH₂ =CHCOOCH₂ CHOHCH₃

CH₂ =CHCOOCH₂ CHNH₂ CH₃

CH₂ =CCH₃ COOCH₂ CH₂ CH₂ NH₂

CH₂ =CHCOOCH₂ CH₂ NH₂

CH₂ =CHCOOCH₂ CH₂ Si(OCH₃)₃

CH₂ =CCH₃ COOCH₂ CH₂ CH₂ Si(OCH₃)₃

CH₂ =CHCOOCH₂ CH₂ COOH

CH₂ =CCH₃ COOCH₂ CH₂ CH₂ CH₂ COOH

CH₂ =CCH₃ COO(CH₂)₆ SH ##STR4##

CH₂ =CH COO CH₂ CH₂ CH₂ CONH₂ ##STR5##

CH₂ =CCH₃ COO CH₂ CH₂ CH₂ COOCH₂ CH₃ ##STR6##

The term "thermoplastic acrylic polymers containing functional groups"as used herein thus includes homopolymers attained from thepolymerization of a substituted acrylic ester or substituted methacrylicester monomer, copolymers obtained from the polymerization of two ormore substituted acrylic ester monomers, copolymers obtained from thepolymerization of two or more substituted methacrylic ester monomers,copolymers obtained from the polymerization of at least one substitutedacrylic ester monomer with at least one substituted methacrylic estermonomer, and copolymers obtained from the polymerization of at least onesubstituted methacrylic ester and/or substituted acrylic ester monomerwith at least one acrylic ester and/or methacrylic ester monomers.

Mixtures of two or more of the aforedescribed homopolymers or copolymerscan also be used in the practice of the present invention.

For acceptable results, the thermoplastic acrylic polymers containingfunctional groups should have a molecular weight of at least 20,000, andpreferably at least 50,000.

The thermoplastic acrylic polymers containing functional groups of theinstant invention differ from thermosettable acrylic polymers in thatthese thermoplastic polymers are formed and applied as primers underconditions such that these functional groups do not react betweenthemselves to effect a cross-linkage between the polymers. Thus, theprimer layer contains thermoplastic acrylic polymers containingfunctional groups.

The thermoplastic acrylic polymers containing functional groups are ingeneral applied as primers from a primer composition containing saidthermoplastic acrylic polymers and a volatile solvent, either organic orinorganic in nature, which is inert, i.e., will not react with thepolycarbonate part to be treated, but which is capable of dissolving thethermoplastic acrylic polymers. Generally, the concentrations of thethermoplastic acrylic polymer in the priming composition ranges fromabout 0.5 to about 25 percent by weight, preferably from about 1 toabout 15 percent. Examples of suitable solvents include ethylene glycoldiacetate, butoxyethanol, methylene-dichloride, 1,2-dichloroethylene,chloroform, benzene and toluene.

The primer compositions of the instant invention may also optionallycontain various flatting agents, ultraviolet light absorbent agents,surface-active agents and thixotropic agents. All of these additives andthe use thereof are well known in the art and do not require extensivediscussions. Therefore, only a limited number will be referred to, itbeing understood that any compounds possessing the ability to functionin such a manner, i.e., as a flatting agent, surface-active agent, andultraviolet light absorbent agents can be used.

The various surface-active agents, including anionic, cationic andnonionic surface-active agents are described in Kirk-Othmer Encyclopediaof Chemical Technology, Vol. 19, Interscience Publishers, New York,1969, pp. 507-593, and Encyclopedia of Polymer Science and Technology,Vol. 13, Interscience Publishers, New York, 1960, pp. 477-486, both ofwhich are references and incorporated herein.

Exemplary ultraviolet light absorbent compounds or stabilizers includethose of the hydroxy benzophenone or benzotriazole series. Examples ofthese are: 2-hydroxy-4-n-octoxybenzophenone, substitutedhydroxyphenylbenzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole,and 2-hydroxy-4-methoxybenzophenone. Further examples of ultravioletlight absorbers which may be used in the practice of this invention maybe found in U.S. Pat. No. 3,043,709. In general, the amount of theultraviolet light absorber may vary from about 0.5 to about 15 percentby weight based upon the weight of the priming composition.

A uniform film of the primer composition is applied onto thepolycarbonate surface by any of the known means such as dipping,spraying, roll-coating and the like. After the formed polycarbonate partis coated with the primer composition, the inert volatile solvent may beremoved by drying the coated article until the volatile solventevaporates, leaving a primer layer or coating containing thethermoplastic acrylic polymer containing functional groups on thepolycarbonate surface to which the primer composition was applied. Thedrying operation may be hastened by the use of drying apparatus such as,for example, a drying oven. Generally, the primer layer is a uniformfilm having a thickness varying between about 0.002 mil to about 1 mil,preferably between about 0.01 mil to about 0.5 mil.

After the polycarbonate article which is to be coated has been primed bythe application of the primer composition and the evaporation of thesolvent component of the primer composition, the primed surface of thepolycarbonate article is then coated with the silica filledorganopolysiloxane coating. In the practice of this invention, a silicafilled organopolysiloxane coating composition containing a furthercurable organopolysiloxane and colloidal silica is applied onto thecured primer and is then cured to form a thermoset silica filledorganopolysiloxane coating.

The silica filled further curable organopolysiloxane top coatcomposition is disclosed in U.S. Pat. Nos. 3,986,997 and 4,027,073 andcomprises a dispersion of colloidal silica in a lower aliphaticalcohol-water solution of the partial condensate of a silanol having theformula

    R.sup.4 Si(OH).sub.3                                       IV.

wherein R⁴ is selected from the group consisting of alkyl radicalscontaining from 1 to 3 carbon atoms, the vinyl radical, the3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and thegamma-methacryloxypropyl radical, with at least 70 percent by weight ofsaid silanol being CH₃ Si(OH)₃. This composition generally contains fromabout 10 to about 50 percent by weight of solids, said solids consistingessentially of a mixture of from about 10 to about 70 percent by weightof colloidal silica and from about 30 to about 90 percent by weight ofthe partial condensate of a silanol. The partial condensate of asilanol, i.e., a siloxanol, is obtained, preferably, entirely from thecondensation of CH₃ Si(OH)₃, however, the partial condensate may alsooptionally be comprised of a major portion which is obtained from thecondensation of CH₃ Si(OH)₃ and a minor portion which is obtained fromthe condensation of monoethyltrisilanol, monopropyltrisilanol,monovinyltrisilanol, mono gamma-methacryloxy-propyltrisilanol, monogamma-glycidoxypropyltrisilanol, or mixtures thereof. The compositionfurther contains sufficient acid to provide a pH in the range of 3.0 to6.0. The pH is maintained in this range in order to prevent prematuregellation and increase the shelf life of the silica filledorganopolysiloxane top coat composition and to obtain optimum propertiesin the cured coating. Suitable acids include both organic and inorganicacids such as hydrochloric, chloroacetic, acetic, citric, benzoic,formic, propionic, maleic, oxalic, glycolic and the like. The acid canbe added to either the silane, which hydrolyzes to form the silanolcomponent of the composition, or the hydrosol prior to mixing the twocomponents.

The trisilanol component of the top coat composition of the presentinvention is generated in situ by the addition of the correspondingtrialkoxysilanes to aqueous dispersions of colloidal silica. Suitabletrialkoxysilanes are those containing methoxy, ethoxy, isopropoxy andt-butoxy substituents. Upon generation of the silanol in the acidicaqueous medium, there is condensation of the hydroxyl substituents toform --Si--O--Si bonding. The condensation is not complete, but ratherthe siloxane retains an appreciable quantity of silicon-bonded hydroxylgroups, thus rendering the organopolysiloxane polymer soluble in thewater-alcohol solvent. This soluble partial condensate can becharacterized as a siloxanol polymer having at least one silicon-bondedhydroxyl group per every three --SiO--units. During curing of the topcoating composition on the primer, these residual hydroxyl groupscondense to give a silsesquioxane, R⁴ SiO_(3/2).

The silica component of the top coat composition is present in the formof colloidal silica. Aqueous colloidal silica dispersions generally havea particle size in the range of 5 to 150 millimicrons in diameter. Thesesilica dispersions are prepared by methods well-known in the art and arecommercially available. It is preferred to use colloidal silica having aparticle size in the range of 10 to 30 millimicrons in diameter in orderto obtain dispersions having a greater stability and to provide topcoatings having superior optical properties.

The silica filled organopolysiloxane top coat compositions are preparedby adding trialkoxysilanes to colloidal silica hydrosol and adjustingthe pH to a range of 3.0 to 6.0 by the addition of acid. As mentionedpreviously, the acid can be added to either the silane or the silicahydrosol before the two components are mixed. Alcohol is generatedduring the hydrolysis of the trialkoxy silanes to the trisilanols.Depending upon the percent solids desired in the final coatingcomposition, additional alcohol, water, or a water-miscible solvent canbe added. Suitable alcohols are the lower aliphatic alcohols such asmethanol, ethanol, isopropanol, t-butanol, and mixtures thereof.Generally, the solvent system should contain from about 20 to about 75weight percent alcohol to ensure solubility of the siloxanol formed bythe condensation of the silanol. If desired, a minor amount of anadditional water-miscible polar solvent such as acetone, butylcellosolve, and the like can be added to the water-alcohol solventsystem. Generally, sufficient alcohol or water-alcohol solvent is addedto give a composition containing from about 10 to about 50 percent byweight of solids, said solids generally comprising from about 10 toabout 70 percent by weight of colloidal silica and from about 30 toabout 90 percent by weight of the partial condensate of the silanol. Thecomposition is allowed to age for a short period of time to ensureformation of the partial condensate of the silanol, i.e., the siloxanol.This condensation occurs upon generation of the silanol in the acidicaqueous medium through the hydroxyl substituents to form Si--O--Sibonding. The condensation is not complete, resulting in a siloxanehaving an appreciable quantity of silicon-bonded hydroxyl group. Thisaged, silica filled further curable organopolysiloxane top coatcomposition is then applied onto the primed polycarbonate by any of thecommonly known methods such as dipping, spraying, flow-coating and thelike. After the top coat composition is applied to the primedpolycarbonate, the polycarbonate is air dried to evaporate the volatilesolvents from the top coat composition. Thereafter, heat is applied tocure the top coat. During curing, the residual hydroxyls of the siloxanecondense to give a silsesquioxane, R⁴ SiO_(3/2). The result is a silicafilled cross-linked organopolysiloxane top coat which is tenaciouslyadhered to the substrate and is highly resistant to scratching,abrasion, chemical solvents, and marring. Generally, the top coatcontains from about 10 to about 70 weight percent silica and from about30 to about 90 weight percent of the organopolysiloxane present as thesilsesquioxane R⁴ SiO_(3/2).

The thickness of the top-coat generally is dependent upon the method ofapplication and upon the weight percent solids present in silica filledfurther curable organopolysiloxane top coat composition. In general, thehigher the percent solids, and the longer the application time, thegreater the thickness of the top coat. It is preferred that the curedtop coat have a thickness of from about 0.1 to about 0.5 mils, morepreferably from 0.15 to about 0.4 mils, and most preferably from about0.2 to about 0.25 mils.

Another embodiment of the present invention is a process of producing amar, abrasion, scratch and chemical resistant polycarbonate article. Theprocess comprises the steps of: (i) applying onto the polycarbonate aprimer composition containing a thermoplastic acrylic polymer containingfunctional groups and a solvent; (ii) evaporating the solvent to leave asolid primer layer containing a thermoplastic acrylic polymer containingfunctional groups on the polycarbonate surface; (iii) applying a silicafilled further curable organopolysiloxane top coat composition onto saidprimer layer, the top coat composition comprising a dispersion ofcolloidal silica in a lower alkanol-water solution of the partialcondensate of a silanol of the formula R⁴ Si(OH)₃ in which R⁴ isselected from the group consisting of alkyl radicals containing from 1to 3 carbon atoms, the vinyl radical, the 3,3,3-trifluoropropyl radical,the gamma-glycidoxypropyl radical and the gamma-methacryloxypropylradical, at least 70 weight percent of the silanol being CH₃ Si(OH)₃ ;(iv) evaporating off the volatile solvents present in the top coatcomposition; and (v) curing the top coating by the application of heatthereto to form a silica filled thermoset organopolysiloxane, i.e., asilsesquioxane.

PREFERRED EMBODIMENT OF THE INVENTION

In order that those skilled in the art may better understand how thepresent invention may be practiced, the following examples are given byway of illustration and not by way of limitation.

EXAMPLE 1

An aromatic polycarbonate is prepared by reacting2,2-bis(4-hydroxyphenol)propane and phosgene in the presence of an acidacceptor and a molecular weight regulator and having an intrinsicviscosity of 0.57. The product is then fed to an extruder, whichextruder is operated at about 265° C. and the extrudate is comminutedinto pellets.

The pellets are then injection molded at about 315° C. into test panelsof about 4 in. by 4 in. by about 1/8 in. thick. The test panels aresubjected to an abrasion test. The abrasion test is one wherein testpanels having a 1/4 inch diameter hole cut in the center are subjectedto a Taber Abraser. The Taber Abraser is equipped with CS-10F wheelswhich are resurfaced every 200 cycles by abrading for 25 cycles on anS-11 refacing disc. The weights used in combination with the CS-10Fwheels are 500 gm. weights. Initial measurements of % Haze are made atfour places around the future wear track of the sample using a GardnerHazemeter. The sample is abraded for 300 cycles, cleaned withisopropanol, and the % Haze is remeasured at the same four places. Thefour differences in % Haze are calculated and averaged to give the Δ%Haze. The results of this abrasion test are set forth in Table II.

EXAMPLE 2

A colloidal silica filled organopolysiloxane top coat compositioncontaining 37 weight percent solids, 50% of which are SiO₂, isformulated by adding a commercially available aqueous dispersion ofcolloidal silica, having SiO₂ of approximately 13-14 millimicronparticle size, to methyltrimethoxysilane which has been acidified by theaddition of 2.5 weight percent glacial acetic acid. This composition ismixed for four hours and is then adjusted to a pH of 3.9 by addition ofmore glacial acetic acid. This acidified composition is then diluted to18% solids by the addition of isopropanol and aged for four days toensure formation of the partial condensate of CH₃ Si(OH)₃.

EXAMPLE 3

This example is designed to illustrate a procedure of the instantinvention for priming and then top coating polycarbonate articles andalso the enhanced abrasion resistant properties obtained thereby.Various primer solutions are made containing 20% solids, which solidsare the acrylic monomers of the instant invention, by combining theacrylic monomers with a catalytic amount of benzoyl peroxide in asolution of 20 parts by weight of ethyleneglycol diacetate and 80 partsby weight of butoxy ethanol and stirring under nitrogen for 24 hours at75°-85° C. The coated solutions are flowed onto polycarbonate panelsprepared in accordance with Example 1, allowed to drain, and heated at250° F. for 15-30 minutes to evaporate the solvent. At this point, thepolycarbonate panels have deposited thereon a thin primer layercontaining a thermoplastic acrylic polymer containing functional groups.The primed test panels are then flow coated with the colloidal silicafilled organopolysiloxane top coat composition prepared substantially inaccordance with Example 2. Excess top coat solution is allowed to drainoff and the coated panels are allowed to air dry for 30 minutes toevaporate off the solvent from the top coating composition. The panelsare then baked for 1 hour at 125° C. to effect the cure of theorganopolysiloxane.

These primed, top coated test panels are subjected to theabove-described abrasion test and to an adhesion test which consists ofusing a multiple blade tool to cut parallel grooves about 1 mm apartthrough the coating into the substrate, rotating the sample 90° andrepeating the cutting process thereby forming a grid pattern of 1 mmsquares cut into the coating, and applying an adhesive tape over thecross-hatched area and quickly pulling said tape off (a sample fails theadhesion test if any of the squares in the grid are pulled off). Thetest panels are also subjected to the sunlamp aging test. This test isone wherein the sample undergoes severe exposure to ultravioletradiation. In the sunlamp aging test, the coated samples are exposed toan RS-sunlamp, and after exposure for a predetermined period of time areremoved and subjected to the adhesion test.

The results obtained from the above tests, as well as the thermoplasticmonomers used in formulating the primer and the thickness of the primercoating are set forth in Table II.

                                      TABLE II                                    __________________________________________________________________________    Thermoplastic                                                                             Thickness, in mils,                                                                    Initial                                                                            % Δ Haze,                                                                     Adhesion, Hours                               Acrylic Polymer                                                                           of Primer                                                                              Adhesion                                                                           300 Cycles                                                                          Exposure to RS Sunlamp                        __________________________________________________________________________    Control of                                                                    Example 1   --       --   34    --                                            95% ethyl   0.05     Pass 2.4   Pass after 426 hours                          methacrylate                                                                  5% γ-methacryloxy-                                                      propyltrimethoxysilane                                                        90% methyl                                                                    methacrylate                                                                              0.15     Pass 5.9   Pass after 521 hours                          10% hydroxyethyl                                                              methacrylate                                                                  96% isobutyl                                                                  methacrylate                                                                              0.26     Pass 6.6   Pass after 766 hours                          5% hydroxyethyl                                                               methacrylate                                                                  97.5% methyl                                                                  methacrylate                                                                              0.3      Pass 5.7   Pass after 426 hours                          1% hydroxyethyl                                                               methacrylate                                                                  97.5% methyl                                                                  methacrylate                                                                              0.4      Pass 5.3   Pass after 521 hours                          2.5% hydroxyethyl                                                             methacrylate                                                                  __________________________________________________________________________

EXAMPLE 4

This example is designed to illustrate the criticality of the particularcombination of the thermoplastic acrylic polymer primer layer containingfunctional groups and silica filled organopolysiloxane top coat inproviding a durable and tenaciously adhered coating effective to producean abrasion resistant polycarbonate article. Unprimed polycarbonatepanels are prepared substantially in accordance with Example 1 and areflow-coated with a silica filled organopolysiloxane top coat compositionprepared substantially in accordance with Example 2. Excess top coatcomposition is permitted to drain off and the coated unprimed testpanels are air dried for 30 minutes to evaporate the solvent, followedby a one-hour bake at 250° F. to cure the further curableorganopolysiloxane. These unprimed coated test panels are subjected tothe aforedescribed adhesion tests (both before and after exposure to theRS sunlamp) and the results are set forth in Table III.

                  TABLE III                                                       ______________________________________                                        Initial          Adhesion after                                               Adhesion         RS sunlamp exposure                                          ______________________________________                                        Marginal*        Fails after 36 hours                                         ______________________________________                                         *The results of the adhesion test before exposure were uneven. That is to     say, some samples failed the adhesion test while other samples passed the     adhesion test.                                                           

As can be seen from Tables II and III, the adhesion, both before andafter exposure to the RS sunlamp, of the colloidal silica filledorganopolysiloxane top coat to the polycarbonate substrate primed inaccordance with the present invention is markedly superior as comparedwith the adhesion of the colloidal silica filled organopolysiloxane topcoat to an unprimed polycarbonate substrate.

EXAMPLE 5

This example is likewise designed to illustrate the criticality of theparticular combination of the thermoplastic acrylic polymer primer layerand silica filled organopolysiloxane top coat in providing a durable andtenaciously adhered coating effective to produce an abrasion resistantpolycarbonate article. EV-6174, a commercially available thermosettableacrylic (32% solids in butanol) available from Bee Chemical Company, isdiluted with n-butanol to various solids concentrations. Into thesesolutions are dipped polycarbonate test panels prepared substantially inaccordance with Example 1. The polycarbonate panels are then removedfrom the priming solutions and are allowed to remain in the open air forabout 30 minutes, during which time the solvent from the primingsolutions evaporates and deposits a thin priming film on thepolycarbonate surface. The primed test panels are then flow coated witha silica filled organopolysiloxane top coat composition preparedsubstantially in accordance with Example 2. Excess top coat compositionis permitted to drain off and the test panels are air dried for 30minutes and are thereafter subjected to 1 hour of heating at 125° C.These primed and top coated test panels are subjected to theaforedescribed adhesion test (both before and after exposure to the RSsunlamp) and to the abrasion test. The results of these tests, as wellas the concentration of the thermosettable acrylic in the primersolution and the thickness of the primer layer are set forth in TableIV.

                  TABLE IV                                                        ______________________________________                                                                             Adhesion                                 % Solids in                                                                            Primer                      after RS                                 n-butanol                                                                              thickness           Initial sunlamp                                  solution (mils)    % Haze    adhesion                                                                              exposure                                 ______________________________________                                        1        0.007     4.4       Pass    Fail after                                                                    96 hours                                 2        0.014     5.9       Pass    Fail after                                                                    96 hours                                 5        0.047     8.3       Pass    Fail after                                                                    96 hours                                 10       0.116     11.2      Pass    Fail after                                                                    96 hours                                 ______________________________________                                    

A comparison of Tables II and IV shows that the instant thermoplasticacrylic polymer containing functional groups primer layer results in acoating having markedly superior durability after exposure to UV-agingunder the RS sunlamp as compared with a coating which contains athermosettable acrylic primer layer. Furthermore, it is apparent fromTable IV that with a thermosettable acrylic primer the abrasionresistance provided by the coating deteriorates as the thickness of theprimer layer increases. This is not the case with the thermoplasticacrylic polymer containing functional groups primers of the presentinvention.

Thus, a particular advantage of the instant thermoplastic acrylicprimers is that abrasion resistance after coating with a silicone topcoat is not a function of primer layer thickness. It is well known tothose skilled in the art that wedging occurs during the coating of largepolycarbonate sheets. Thus, it is a great advantage if a property suchas abrasion resistance is not dependent upon primer coating thickness.

A further advantage of having a thick primer coating is that ultravioletlight and other stabilizers can effectively be incorporated in thecoating. Polycarbonate generally undergoes photodegradation and turnsyellow during prolonged weathering. However, if the surface ofpolycarbonate can be protected from ultraviolet light, it can bestabilized against photodegradation. Incorporation of ultravioletlight-absorbers in a coating on polycarbonate is therefore highlydesirable since these materials will screen ultraviolet light fromreaching the surface of the polycarbonate. For practical purposes,however, a coating must generally be at least about 0.2-0.3 mils thickto contain enough of an ultraviolet light-absorber so that enoughultraviolet light, for example more than 90% of the incident ultravioletlight, can be screened from the surface of the polycarbonate. Thinnerprimer coatings theoretically require much more ultravioletlight-absorbers to effectively screen more than 90% of incidentultraviolet light. Due to the fact that the primer layers of the instantinvention can be relatively thick, since abrasion resistance is notdependent upon primer coating thickness, ultraviolet light-absorbers cantherefore be effectively incorporated in the thermoplastic acrylicprimers of the instant invention.

The foregoing disclosure of this invention is not to be considered aslimiting, since many variations may be made by those skilled in the artwithout departing from the scope or spirit of the foregoing description.For example, although the above examples are limited to only a few ofthe very many thermoplastic acrylic polymers which can be employed inthe present invention, it should be understood that the presentinvention includes a much broader class of such polymers as shown byformula III and the description preceding these examples.

What we claim as new and desire to secure by Letters Patent of theUnited States is:
 1. A shaped non-opaque coated polycarbonate articlehaving improved abrasion and chemical solvent resistance comprising apolycarbonate substrate having on at least one surface thereof (i) anadhesion promoting primer layer consisting essentially of athermoplastic acrylic polymer containing functional groups; and (ii)having disposed on said primer layer a tenaciously and durably adheredtop coat consisting essentially of a colloidal silica filled thermosetorganopolysiloxane which is the condensation product of a silanol of theformula RSi(OH)₃ in which R is selected from the group consisting ofalkyl radicals of 1 to 3 carbon atoms, the vinyl radical, the3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and thegamma-methacryloxypropyl radical, at least 70 weight percent of thesilanol being CH₃ Si(OH)₃ .
 2. The article of claim 1 wherein saidprimer layer contains an ultraviolet light absorber.
 3. The article ofclaim 1 wherein said thermoset colloidal silica filledorganopolysiloxane contains from about 10 to about 70 weight percent ofcolloidal silica.
 4. The article of claim 1 wherein said thermosetcolloidal silica filled organopolysiloxane is the condensation productof CH₃ Si(OH)₃.
 5. The article of claim 4 wherein said thermosetcolloidal silica filled organopolysiloxane contains from about 10 toabout 70 weight percent of colloidal silica.
 6. The article of claim 1wherein said functional groups are selected from the class consisting ofhydroxyl, carboxyl, amine, epoxide, amide, SH, SO₃ H, COOR² and Si(OR³)₃groups wherein R² and R³ represent alkyl groups containing from 1 toabout 20 carbon atoms.
 7. The article of claim 6 wherein saidthermoplastic acrylic polymer containing functional groups is acopolymer obtained by the copolymerization of at least one monomerselected from the class consisting of acrylic ester monomers andmethacrylic ester monomers with at least one monomer selected from theclass consisting of substituted acrylic ester monomers and substitutedmethacrylic ester monomers.
 8. The article of claim 6 wherein saidthermoplastic acrylic polymer containing functional groups is obtainedby the polymerization of at least one monomer selected from the classconsisting of acrylic ester monomers containing functional groups andmethacrylic ester monomers containing functional groups.
 9. A non-opaquecoated polycarbonate article having improved abrasion and chemicalsolvent resistance comprising a polycarbonate substrate having on atleast one surface thereof (i) an adhesion promoting primer layerconsisting essentially of a thermoplastic acrylic polymer containingfunctional groups; and (ii) a tenaciously and durably adhered top coaton said primer layer consisting essentially of the cured product of acomposition consisting essentially of a dispersion of colloidal silicain a lower aliphatic alcohol-water solution of the partial condensate ofa silanol of the formula RSi(OH)₃ wherein R is selected from alkylradicals containing from 1 to 3 carbon atoms, the vinyl radical, the3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and thegamma-methacryloxypropyl radical, at least 70 weight percent of thesilanol being CH₃ Si(OH)₃, said composition containing 10 to 50 weightpercent solids consisting essentially of 10 to 70 weight percentcolloidal silica and 30 to 90 weight percent of the partial condensate,said composition containing sufficient acid to provide a pH in the rangeof 3.0 to 6.0.
 10. The article of claim 9 wherein said thermoplasticacrylic polymer containing functional groups is obtained by thepolymerization of at least one monomer represented by the generalformula H₂ C═CYCOOR¹ X wherein Y is a hydrogen or a methyl radical, R¹is a divalent saturated aliphatic hydrocarbon radical containing from 1to about 20 carbon atoms, and X is selected from the class consisting ofhydroxyl, carboxyl, amine, epoxide, amide, SH, SO₃ H, COOR², andSi(OR³)₃ radicals wherein R² and R³ represent alkyl radicals containingfrom 1 to about 20 carbon atoms.
 11. The article of claim 9 wherein saidprimer layer contains an ultraviolet light screening agent.
 12. Thearticle of claim 9 wherein said thermoplastic acrylic polymer containingfunctional groups is a copolymer obtained by the polymerization of (i)at least one monomer represented by the general formula H₂ C═CYCOOR¹ Xwherein Y is hydrogen or a methyl radical, R¹ is a divalent saturatedaliphatic hydrocarbon group containing from 1 to about 20 carbon atoms,and X is selected from the class consisting of hydroxyl, carboxyl,amine, epoxide, amide, SH, SO₃ H, COOR² and Si(OR³)₃ groups wherein R²and R³ represent alkyl radicals containing from 1 to about 20 carbonatoms; with (ii) at least one monomer represented by the general formulaH₂ C═CY'COOR⁴ wherein Y is hydrogen or a methyl radical, and R⁴ is analkyl radical containing from 1 to about 20 carbon atoms.
 13. Thearticle of claim 12 wherein (i) is γ-methacryloxypropyltrimethoxy silaneand wherein (ii) is ethyl methacrylate.
 14. The article of claim 12wherein (i) is hydroxyethyl methacrylate.
 15. The article of claim 14wherein (ii) is isobutyl methacrylate.
 16. The article of claim 14wherein (ii) is methyl methacrylate.
 17. A non-opaque coatedpolycarbonate article comprising a polycarbonate substrate having on atleast one surface thereof (i) an adhesion promoting primer layerconsisting essentially of a thermoplastic acrylic polymer containingfunctional groups; and (ii) a top coat composition disposed on saidprimer layer, said top coat composition consisting essentially of adispersion of colloidal silica in a lower aliphatic alcohol-watersolution of the partial condensate of a silanol of the formula RSi(OH)₃in which R is selected from the group consisting of alkyl radicals of 1to 3 carbon atoms, the vinyl radical, the 3,3,3-trifluoropropyl radical,the gamma-glycidoxypropyl radical and the gammamethacryloxypropylradical, at least 70 weight percent of the silanol being CH₃ Si(OH)₃,said composition containing 10 to 50 weight percent solids consistingessentially of 10 to 70 weight percent colloidal silica and 30 to 90weight percent of the partial condensate, said composition containingsufficient acid to provide a pH in the range of 3.0 to 6.0.
 18. Thearticle of claim 17 wherein said primer layer contains an ultravioletlight absorber.
 19. The article of claim 17 wherein said thermoplasticacrylic polymer containing functional groups has a molecular weight ofat least 15,000.
 20. The article of claim 19 wherein said thermoplasticacrylic polymer containing functional groups is obtained by thepolymerization of (i) at least one monomer represented by the generalformula H₂ C═CYCOOR¹ X wherein Y is hydrogen or a methyl radical, R¹ isa divalent saturated aliphatic hydrocarbon radical containing from 1 toabout 20 carbon atoms, and X is selected from the class consisting ofhydroxyl, carboxyl, amine, epoxide, amide, SH, SO₃ H, COOR² and Si(OR³)₃groups wherein R² and R³ represent alkyl radicals containing from 1 toabout 20 carbon atoms, with (ii) at least one monomer represented by thegeneral formula H₂ C═CY'COOR⁴ wherein Y' is hydrogen or a methylradical, and R⁴ is an alkyl radical containing from 1 to about 20 carbonatoms.
 21. The article of claim 19 wherein said thermoplastic acrylicpolymer containing functional groups is obtained by the polymerizationof at least one monomer represented by the general formula H₂ C═CYCOOR¹X wherein Y is hydrogen or a methyl radical, R¹ is a bivalent saturatedaliphatic hydrocarbon radical containing from 1 to about 20 carbonatoms, and X is selected from the class consisting of hydroxyl,carboxyl, amine, epoxide, amide, SH, SO₃ H, COOR² and Si(OR³)₃ radicalswherein R² and R³ represent alkyl radicals containing from 1 to about 20carbon atoms.
 22. A shaped non-opaque coated polycarbonate articlehaving improved abrasion and chemical solvent resistance comprising apolycarbonate substrate having on at least one surface thereof (i) anadhesion promoting primer layer consisting essentially of (A) athermoplastic acrylic polymer containing functional groups, and (B) atleast one ultraviolet light screening compound; and (ii) having disposedon said primer layer a tenaciously and durably adhered top coatconsisting essentially of a colloidal silica filled thermosetorganopolysiloxane which is the condensation product of a silanol of theformula RSi(OH)₃ in which R is selected from the group consisting ofalkyl radicals of 1 to 3 carbon atoms, the vinyl radical, the3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and thegamma-methacryloxypropyl radical, at least 70 weight percent of thesilanol being CH₃ Si(OH)₃.
 23. The article of claim 22 wherein saidacrylic polymer containing functional groups is obtained by:(i) thepolymerization of at least one monomer represented by the generalformula H₂ C═CYCOOR¹ X with at least one monomer represented by thegeneral formula H₂ C═CY¹ COOR⁴ ; or, (ii) the polymerization of at leastone monomer represented by the general formula H₂ C═CYCOOR¹ X, wherein Yand Y¹ independently represent a hydrogen or a methyl radical, R¹represents a divalent saturated aliphatic hydrocarbon radical containingfrom 1 to about 20 carbon atoms, R⁴ represents an alkyl radicalcontaining from 1 to about 20 carbon atoms, and X is selected from theclass consisting of hydroxyl, carboxyl, amine, epoxide, amide, SH, SO₃H, COOR² and Si(OR³)₃ radicals wherein R² and R³ represent alkylradicals containing from 1 to about 20 carbon atoms.
 24. The article ofclaim 23 wherein said thermoset colloidal silica filledorganopolysiloxane contains from about 10 to about 70 weight percent ofcolloidal silica.
 25. A shaped non-opaque coated polycarbonate articlehaving improved abrasion and chemical solvent resistance comprising apolycarbonate substrate having disposed on at least one surface thereof(i) an adhesion promoting primer layer consisting essentially of (A) athermoplastic acrylic polymer containing functional groups, and (B) atleast one ultraviolet light screening compound; and (ii) having disposedon said primer layer a tenaciously and durably adhered top coatconsisting essentially of the cured product of a composition consistingessentially of a dispersion of colloidal silica in a lower aliphaticalcohol-water solution of the partial condensate of a silanol of theformula RSi(OH)₃ in which R is selected from the group consisting ofalkyl radicals of 1 to 3 carbon atoms, the vinyl radical, the3,3,3-trifluoropropyl radical, the gamma-glycidoxypropyl radical and thegamma-methacryloxypropyl radical, at least 70 weight percent of thesilanol being CH₃ Si(OH)₃, said composition containing 10 to 50 weightpercent solids consisting essentially of 10 to 70 weight percentcolloidal silica and 30 to 90 weight percent of the partial condensate,said composition containing sufficient acid to provide a pH in the rangeof 3.0 to 6.0.
 26. The article of claim 25 wherein said acrylic polymercontaining functional groups is obtained by:(I) the polymerization of atleast one monomer represented by the general formula H₂ C═CYCOOR¹ X withat least one monomer represented by the general formula H₂ C═CY¹ COOR⁴ ;or, (II) the polymerization of at least one monomer represented by thegeneral formula H₂ C═CYCOOR¹ X, wherein Y and Y¹ independently representa hydrogen or a methyl radical, R¹ represents a divalent saturatedaliphatic hydrocarbon radical containing from 1 to about 20 carbonatoms, R⁴ represents an alkyl radical containing from 1 to about 20carbon atoms, and X is selected from the class consisting of hydroxyl,carboxyl, amine, epoxide, amide, SH, SO₃ H, COOR² and Si(OR³)₃ radicalswherein R² and R³ represent alkyl radicals containing from 1 to about 20carbon atoms.